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IDT Switch Partitions
Notes
PES48H12G2 User Manual
A port in the upstream switch port mode has the following behavior.
– Has the behavior of an upstream switch port defined by the PCI express base specification.
– The LTSSM is operational and behaves as an upstream port.
Downstream Switch Port
A port in downstream switch port mode behaves as the downstream port of a switch partition. The PCI-
to-PCI bridge associated with a downstream switch port has an associated type 1 header. A port in the
downstream switch port mode has the following behavior.
– Has the behavior of a downstream switch port defined by the PCI express base specification.
– The LTSSM is operational and behaves as a downstream port.
The Device Number (DEVNUM) field in the SWPORTxCTL register determines the device number of
the downstream port within the switch partition. The function number of a downstream switch port is always
zero. The behavior when two or more downstream switch ports in the same partition are configured with the
same device number is undefined.
Since partitions are independent, two downstream switch ports in different partitions may share the
same device number. If the DEVNUM field is modified using a PCI configuration write request, then the
modification takes place prior to the generation of a completion for the request. The completion uses the old
(i.e., unmodified) device number.
Modifying the DEVNUM field using a PCI configuration write request does not modify the bus and device
numbers captured by the PCI-to-PCI bridge. Therefore, a subsequent Type 0 configuration write must be
performed to a PCI-to-PCI bridge following modification of its device number.
– Failure to follow this procedure will result in an incorrect value in the requester and completer ID
fields of TLPs generated by the PCI-to-PCI bridge.
As expected, modifying the DEVNUM field via SMBus or Serial EEPROM does not modify the bus and
device numbers captured by the PCI-to-PCI bridge.
Port Operating Mode Change
The operating mode of a port is determined by the Port Mode (MODE), Switch Partition (SWPART), and
Device Number (DEVNUM) fields in the SWPORTxCTL register as well as in some cases the state (STATE)
field in the corresponding partition control (SWPARTxCTL) register. The initial operating mode of a port is
determined by the switch mode setting in the boot configuration vector sampled during a switch funda-
mental reset.
The following events constitute a port operating mode change and initiate the action specified by the
Operating Mode Change Action (OMA) field in the corresponding SWPORTxCTL register.
– Any modification of the value in the MODE, SWPART, or DEVNUM fields in the SWPORTxCTL
register.
• A write of the same value already contains in these fields does not result in a port operating
mode change.
– Setting the STATE field in the SWPARTxCTL register of the partition with which the port is asso-
ciated to disabled.
When a port is disabled due to the STATE field in the corresponding partition SWPARTxCTL field being
set to disabled, modification of values in the MODE, SWPART, or DEVNUM fields that do not modify the
partition with which the port is associated result in the actions associated with an operating mode change
(e.g., OMCI and OMCC are set), but the port remains in the disabled mode during and after the operating
mode change process.
The modification of the MODE field to disabled causes the port to detach from the disabled partition;
however, the port remains in the disabled mode. All of the actions associated with an operating mode
change (e.g., OMCI and OMCC are set) continue to operate as described above. The modification of the
SWPART field causes the port to detach from the disabled partition. The new operating mode is dependent
on the MODE field and the state of the new partition with which the port is associated (if any).
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April 5, 2013
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